• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.94-97
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• 2002

Micromolding methods are most suitable for mass production of plastic microlens and lens array with low cost. Among the procedures related with micromolding of microlens array, fabrication of mold insect which contains micro cavity of lens shape is the most important stage. In this study, nickel mold inserts for 45 $\mu\textrm{m}$ and 95 $\mu\textrm{m}$ diameters lens way were fabricated using electroforming process. The mother for metal mold inset was made using reflow method. A micro compression molding with polymer powders was used to test the qualities of the metal mold insets. Micro lens profile and surface roughness was measured by interferometric technique and AFM, respectively. The final molded lens replicated the mother well, and had good surface quality.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.11
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• pp.1897-1906
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• 2003

A finite element analysis for near-net-shape forming of A16061 powder was performed under warm rubber isostatic pressing and warm die pressing. The advantages of warm compaction by rubber isostatic pressing were discussed to obtain a part with better density distributions. The shape of rubber mold was designed by determining a cavity shape that provides a desired shape of the final powder compact. To simulate densification and deformed shape of a powder compact during pressing, the elastoplastic constitutive equation based on yield function of Shima-Oyane was implemented into a finite element program(ABAQUS). The hyperelastic constitutive equation based on the Ogden strain energy Potential was employed to analyze nonlinear elastic response of rubber. Finite element results were compared with experimental data for Al6061 powder compacts under warm die pressing and warm isostatic pressing.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.45 no.4
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• pp.233-239
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• 2022

The injection molding process is a process in which thermoplastic resin is heated and made into a fluid state, injected under pressure into the cavity of a mold, and then cooled in the mold to produce a product identical to the shape of the cavity of the mold. It is a process that enables mass production and complex shapes, and various factors such as resin temperature, mold temperature, injection speed, and pressure affect product quality. In the data collected at the manufacturing site, there is a lot of data related to good products, but there is little data related to defective products, resulting in serious data imbalance. In order to efficiently solve this data imbalance, undersampling, oversampling, and composite sampling are usally applied. In this study, oversampling techniques such as random oversampling (ROS), minority class oversampling (SMOTE), ADASYN(Adaptive Synthetic Sampling), etc., which amplify data of the minority class by the majority class, and complex sampling using both undersampling and oversampling, are applied. For composite sampling, SMOTE+ENN and SMOTE+Tomek were used. Artificial neural network techniques is used to predict product quality. Especially, MLP and RNN are applied as artificial neural network techniques, and optimization of various parameters for MLP and RNN is required. In this study, we proposed an SA technique that optimizes the choice of the sampling method, the ratio of minority classes for sampling method, the batch size and the number of hidden layer units for parameters of MLP and RNN. The existing sampling methods and the proposed SA method were compared using accuracy, precision, recall, and F1 Score to prove the superiority of the proposed method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.426-430
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• 2008

Hot shear-welding is a process of bonding two plates together by using shearing stress in a controlled manner. This study dealt with the hot shear-welding process of two aluminum plates. These two plates were piles up in the shear-welding mold. Due to the shearing stress, these two plates were cut off longitudinally, and meantime they were welded together. During this process the control of the surplus material flow is very important, and it can be realized by designing the overlapping length and the shape of the cavity. The commercial software Deform-3D was employed to predict the effect of these two factors. The overlapping length and the shape of the cavity that presents the optimum design was then developed to get a good shear-welding process.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.4
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• pp.357-364
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• 2017

Metal casting is a process in which molten metal or liquid metal is poured into a mold made of sand, metal, or ceramic. The mold contains a cavity of the desired shape to form geometrically complex parts. The casting process is used to create complex shapes that are difficult to make using conventional manufacturing practices. For the optimal casting process design of sleeve parts, various analyses were performed in this study using commercial finite element analysis software. The simulation was focused on the behaviors of molten metal during the mold filling and solidification stages for the precision and sand casting products. This study developed high-life sleeve parts for the sink roll of continuous hot-dip galvanizing equipment by applying a wear-resistant alloy casting process.

• Journal of Korea Foundry Society
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• v.32 no.2
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• pp.65-74
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• 2012

In this paper, we present the results of our studies on optimal die design towards development of a vacuum die casting process to fabricate fuel cell bipolar plate with micro-channel array. Cavity and overflow shape is designed by computational filling analysis of MAGMA soft. Optimal die design consists of seven overflows at the end of cavity and three overflows at each side wall of cavity. The molten metal that passed the gate and reached the side wall flowed into the side overflow, no turbulent flow occurred, and the filling behavior and velocity distribution were uniform. In addition, partially solidified molten metal passing through the channel was perfectly eliminated by overflow without back-flow. When vacuum pressure, injection speed of low and high region was 300 mbar, 0.3 m/s and 2.5 m/s respectively with Silafont 36 die casting alloy, sound sample without casting defects was obtained. The experimental results are nearly consistent with simulation results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.511-517
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• 2016

Current oil-type potential transformers for trains are filled with insulating oil, which could have problems like explosions due to rising inner pressure during train operation. Therefore, mold and dry-type potential transformers are being developed to prevent explosions. One problem in manufacturing mold-type transformers is preventing void formation around the coiled core inside the mold during epoxy filling, which could cause an electrical spark. Micro voids can remain in the resin after filling, and macro voids can occur due to the structure shape. A transformer that is being developed has a cavity at the junction of the core and the coil for better performance, and when highly viscous epoxy flows inside the cavity channel, macro voids can form inside it. Therefore, in this study, the free-surface flow of the mold filling procedure was analyzed numerically by applying the VOF method. The results were used to understand the phenomena of void formation inside the cavity and to modify the process conditions to reduce voids.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.02a
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• pp.253-259
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• 2002

Micro cell structures with high aspect ratio were fabricated by injection molding method. The mold inserts had dimension $1.9cm\times8.3cm$ composed of a lot of micro posts and were fabricated by LIGA process. The size of the micro posts was $157{\mu}m\times157{\mu}m\times500{\mu}m$ and the gaps between two adjacent posts were $50{\mu}m$. Using Polymethylmethacrylate (PMMA) injection molding was performed. The key experimental variables were temperature, pressure, and time. By controlling these, good shaped mim cell structures with $50{\mu}m$ in wall thickness and $500{\mu}m$ in depth were obtained. In order to understand micro molding mechanism, shape changes of molded PMMA were studied with experimental variables. And the durability of mold insert was investigated, too. The results show that the most important factor in molding processes was the mold temperature that is closely related to the filling of the melt into the micro cavity. And the holding time before cooling showed a great effect on the quality of molded PMMA.

• Journal of Korea Foundry Society
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• v.31 no.2
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• pp.71-78
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• 2011

This study aims to investigate the formability of bipolar plates for fuel cell fabricated by vacuum die casting of ALDC 6. Cavity shape of mold is thin walled plate (size: $200mm{\times}200mm{\times}0.8mm$) with a serpentine channel (active area: $50mm{\times}50mm$). Before bipolar plate was made by HPDC, computational filling behavior and solidification was performed by MAGMA soft. The final mold design for location and direction of channel was determined by computational simulation. Also, according to injection speed conditions, simulation result was compared to actual die casting experimental result. When vacuum pressure, injection speed of low and high region is 350 mbar, 0.3 m/s and 2.5 m/s respectively, products had few casting defects. On the other hand, at the same as injection speed, without vacuum pressure, products had many casting defects between end of the channel and overflow.

• Journal of computational fluids engineering
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• v.18 no.3
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• pp.20-25
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• 2013

In various manufacturing industries, an in-mold decoration (IMD) process for plastic objects is widely utilized because a film forming and an injection molding processes run simultaneously. In the present study, the deformation of polymer film and filling of resin in the IMD process were numerically investigated to evaluate the quality of the plastic object formed by the IMD process, which consists of thermoforming and injection molding processes. To obtain the initial shape of the polymer film during the injection molding process, the deformation of the polymer film in the thermoforming process was pre-formed using the vacuum conditions to attach the film to a cavity. Since the properties and deformation of polymer film are greatly affected by the behavior of polymer resin being injected into a mold cavity, numerical simulations for the injection molding and film forming were performed with one-way coupling method. The results showed that the injected resin could lead to the tearing of the polymer film in local regions near the corners. In order to verify the proposed numerical methodology, the numerical results of the deformation patterns printed on the initial polymer film were compared with the experimental data. The proposed methodology to couple film forming analysis with injection molding analysis can be used to predict the deformation of film in IMD process.